Figure 4. A, linear representation of three types of gene content from the partial cytochrome b (Cyt b) to 12S rRNA in the mitochondrial (mt) genome of the mackerel icefish. Black and dark grey arrows respectively represent the first and the second duplicates. The first duplicate of the type-1 genome contains full-length nicotinamide adenine dinucleotide (reduced form) dehydrogenase subunit 6 (ND6) and tRNAGlu. Type-2 contains a half-sized ND6 only. Type-3 does not contain ND6 or tRNAGlu. B, PCR amplifications for detecting ND6 and tRNAGlu in the three types of mt genome of the mackerel icefish. PCR fragments between Cyt b and control region (CR) 2 (Cyt b-CR2) and between CR2 and CR3 (CR2-CR3) contain the first and second copies of ND6, respectively. The PCR fragment between ND5 and Cyt b (ND5-Cyt b) did not contain ND6 or tRNAGlu. M, size marker. Lanes 1, 2, 7, and 10 are type-1 individuals. Lanes 3, 4, 8 and 11 are type-2 individuals. Lanes 5, 6, 9, and 12 are type-3 individuals. Abbreviations: E, tRNAGlu; F, tRNAPhe; P, tRNAPro; T, tRNAThr.